metamorphic

Biotite-rich mica schist

Mica schist, dominated by biotite mica (K(Mg,Fe)₃AlSi₃O₁₀(F,OH)₂) with quartz and feldspar

AI-generated identification · may be incorrect

Dark brown-black, sparkly, platy and foliated, with vitreous to pearly luster; biotite has Mohs hardness 2.5–3 and perfect basal cleavage, while associated quartz is harder (7). The image is consistent with a small broken fragment, though exact identification requires testing.

Identified September 16, 2026More metamorphic →

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Physical properties

Formation & geological history

Forms when shale or other clay-rich sediment is regionally metamorphosed under elevated temperature and pressure, commonly during mountain building. Its age depends on the source terrain and may range from Precambrian to relatively young Paleozoic–Mesozoic examples.

Uses & applications

Used mainly as a decorative or educational specimen; crushed mica has limited industrial use as filler, insulation, and drilling-mud additive. It is not generally a construction stone or high-value gemstone.

Geological facts

Foliation results from alignment of mica flakes, allowing the rock to split into shiny layers. Biotite commonly darkens metamorphic rocks compared with muscovite-rich schists.

Field identification & locations

Look for visible aligned mica flakes, easy splitting along foliation, and a dark glittery surface; a streak, hardness, and acid test help distinguish it from graphite-bearing rock or ore. Common in metamorphic belts worldwide, including the Appalachians, Alps, and Himalaya.